After migrating to Struts 2 from WebWork 2, some Actions suddenly exposes "HTTP Status 404 ... The requested resource is not available."
If the Actions utilize the "action!alias" sytax, add the line struts.compatabilityMode.webwork=true
to the struts.properties
file.
The bang syntax is deprecated, so rework the actions before updating to the next Struts 2 release.